GaP-ZnS Multilayer Films: Visible-Light Photoelectrodes by Interface Engineering

In the field of solar water splitting, searching for and modifying bulk compositions has been the conventional approach to enhancing visible-light activity. In this work, manipulation of heterointerfaces in ZnS-GaP multilayer films is demonstrated as a successful alternative approach to achieving visible-light-active photoelectrodes. The photocurrent measured under visible light increases with increasing number of interfaces for ZnS-GaP multilayer films with
the same total thickness, indicating it to be a predominantly interface-driven effect. The activity extends to long wavelengths (650 nm), much longer than expected for pure ZnS, and also longer than previously reported for GaP. Density functional theory (DFT) calculations of ZnS-GaP multilayers predict the presence of electronic states associated with atoms at the interfaces between ZnS and GaP that are different from those found within the layers away from the interfaces; these states, formed due to unique bonding environments found at the
interfaces, lead to a lowering of the band gap and hence the observed visible-light activity.
The presence of these electronic states attributed to the interfaces is confirmed by depthresolved X-ray photoelectron spectroscopy. Thus, we show that interface engineering is a promising route for overcoming common deficiencies of individual bulk materials caused by both wide band gaps and indirect band gaps, and hence enhancing visible-light absorption and photoelectrochemical performance